Electrooptical reproducer



April 29, 1941. J. c. BATCHELOR ELECTROOPTICAL REPRODUCER Filed Aug. 19, 1937 'lll Illl INVENTOR. $6 5111"" in producing Patented -Apr. 29, 1941 UNITED STATES PATENT- waits 2,239,769 sLnoTnoomoAL asrnonuosn John C. Batchelor, Hastings on Hudson, N. Y. t

Application August 19, 1937, Serial No. 159,814

7 Claims.

My invention relates to improvements in television scanning devices and the method of operation thereof.

' One form of scanning device for television reception comprises a cathode ray tube in. which a ray of electrons is focused on a screen and deflected to scan the latter to produce a visible ima'ge,the intensity of the ray being varied in accordance with the received picture signals. The image is viewed either directly or is projected and enlarged by a suitable optical system upon a relatively remote screen. In the latter case, the visibility and degree of enlargement of the image depends upon the brilliancy of the image on the screen of the cathode ray tube. Various constructions and methods of operation have been proposed for the purpose of increasing the brilliancy of the image for projection upon a remote screen. One form of such a cathode ray receiving tube is disclosed in British Patent No. 452,368,

in which the screen metallic sheet of electrons to heat to luminescence the respective elemental areas of this screen in accordance with the intensity of the ray-which is made to vary in accordance with the received picture sigis in the form of a very thin v nals. While this and other forms of construction proposed heretofore have contributed to the possibll ityof producing an image ofgreat brilliancy for projection, there are still limitations in the size to which the image can be-projected on a remote screen, and diiiiculties are still encountered a sufiiciently intense and concentrated electron ray to reproduce a high definition image.

With the foregoing in mind, it is one of the objects of my invention to provide an improved construction and method of operation for a cathode ray scanning device for television reception which, under substantially the same operating conditions, produces on the screen within the tube an image of substantially greater brilliancy than is possible with the various forms of devices proposed heretofore for the same purpose.

Other objects and advantages willappear in the description of my invention which follows.

In accordance with my invention, a cathode ray tube is provided with an image screen, any elemental area of which can be heated to luminescence upon bombardment of such area by electrons focused on the screen. Interposed between this image screen and the electron gun is a'therinionic cathode in the form of a .screen parallel to the image screen and which is scanned by the electron ray. When the electron ray is gr foil which is scanned by the ray provided with ascreen and is characterized directed at any particular elemental area of the cathode screen, this area is substantially instantaneously heated to a temperature correponding to the intensity of the ray at the instant, as controlled by the picture signals, and electrons are emitted from the side of -this area adjacent the image screen and are caused to bombard the adjacent and corresponding elemental area of the image screen to excite the latter to luminescence and. to a. degree substantially proportional-to the ray intensity at the instant. After the ray is deflected away from this elemental area of the cathode screen, electrons still continue'to be emitted from the far side of this area until it cools to the temperature at which electron emission ceases, all of which takes place substantially within a picture interval. Because of the fact that there is this substantial increase in the period of time during which electrons from any elemental area of the cathode screen bombard the corresponding elemental area of the image screen, there is a substantial and corresponding increase in the brilliancy of the image on the latter.

. My invention resides in the improved construction andmethod of operation of the character hereinafter described and claimed.

For the purpose of illustrating my invention, an embodiment thereof is shown in the drawing, wherein:

Figure 1 is a, simplified, diagrammatic view of a cathode ray tube for television reception, constructed and operating in accordance with my invention;

Figure 2 is an enlarged, fragmentary view, taken from Figure'l, and illustrative of the principle of operation; and

Figure 3 is a view similar to Figure 1, showing a modification.

With reference to the drawing, my improved scanning device comprises an evacuated tube I0 l2 and with means in the formof an electron gun it for developing a ray l6 of electrons and directing the ray at the screen l2.

The screen I 2 is made of very fine wire mesh by the fact that bombardment of any elemental area -A thereof by electrons causes such area to be heated to luminescence.

- Disposed between the electron gun I4 and the screen l2, and closely adjacent the latter, is a lhermionic cathode in the form of an electron emisslve screen. 18 of fine wire mesh. The screen l8 may be made, for example, or fine nickel wire strike the screen I 2 and may be coated with a mixture of barium and strontium carbonates so that, when heated by the bombardment of the ray ii, the screen l8 will reach a temperature at which electronic emission takes place.

The ray ii of electrons is deflected horizontally by' coils 20 and vertically by coils 22 to cause it to scan the thermionic cathode l8.

The received picture signals are applied to a control grid or electrode 24 with which the electron gun is provided, to vary the intensity of the ray IS in accordancewith these signals.

- The ray IB'is focused on the screen l8 by an anode 28 in the form ofv a metallic coating on the inside surface of the tube I0.

The thermionic cathode screen l8 and the anode 28 are at a potential which is positive with respect to and substantially greaterthan the potential on the anode 28 of the electron gun, as represented in the drawing, whereby the velocity of the electrons, when they strike or bombard any elemental area of the-screen I8, is sumciently great to cause such area to be heated tov a temperature at which electronic emission takes place from the side of this area adjacent the image screen l2, as represented by the arrows 30 in Figure' 2. Thus, a thermal image may be said to 'be deposited on the cathode-screen l8 by the oathode ray l6.

The screen I2 is at a potential positive with respect to and substantially greater than the potential of the screen It, as represented in the drawing, whereby the electrons 30 are caused to at a relatively high velocity and heat the elemental area A of this screen to luminescence.

In operation, the brilliancy of any elemental area A of the screen I2 is proportional to that part of the picture interval 'during which the electrons 30 continue to flow, and also to the mean intensity of these electrons during such time. These two factors are proportional'to the temperature to which the adjacent and complementary elemental area of the thermionic cathode IB is heated upon bombardment 01' such area by the electron ray l6.

The construction'of the screen I8 is such that, for the condition of maximum intensity 01' the ray IS, the period elapsing before any elemental area of this screen cools to the temperature at the ray I6 is deflected away from this area, equals substantially a picture interval. Also, for the condition of maximum intensity of the my I 6, the period elapsing before the elemental areas A of the screen l2 cool to the temperature at which they-are not visible due'to luminescence, equals substantially a picture interval.

If it is desirable, in any particular case, to space the screens|2 and I8 further apart than is shown in Figure 1, because of the relatively high potential diilerence between these screens or for any other reason, a focusing coil 34 may be used as shown in Figure 3 to develop an electromagnetic focusing field between the screens l2 and I8 whereby each of the individual rays of the electrons 30 is always directedat and focussed on the corresponding elemental area Aof the screen I2. The construction and method of operation in Figure 3 is, otherwise, the same as in Figures '1 and 2.

From the foregoing it will be seen that in my improved scanning'device, the brilliancy of any elemental area of the screen I2 is substantially greater, for the same conditions of intensity of which electronic emission therefrom ceases after the ray I6, than is the case in devices proposed heretofore for the same puipose, and that this is due to the fact that electronic bombardment of the respective elemental areas of the screen I 2 persists or continues after the scanning ray i8 is deflected away from the adjacent and complementary areas of the cathode screen I 8. At the same time, image flicker is substantially eliminated. r

From the foregoing, one of the broader aspects of my invention may be seen to reside in my improved method of operation which consists in successively exciting the respective elemental areas of a screen, such as the elemental areas A of the screen, I2, and during each picture interval varying both the intensity and the duration of excitation of said areas of the screen to produce thereon an image. For example, in the disclosed embodiment of my invention, during each picture interval both the intensity and the duration of excitation of any particular elemental area A vary with and are proportional to both the intensity of the electron ray 30 and the duration of this ray during any picture interval, as controlled or determined by the intensity of the scanning ray or agent H5 at the instant the latter strikes or bombards that elemental area of the screen i8 directly opposite and complementary to the elemental area A of the screen [2.

Another aspect of my invention resides in the heating of the respective elementalareas of a screen to luminescence to produce a visible image on this screen, such as the screen [2, scanning a thermionic cathode for such purpose, such as the cathode screen [8, and controlling the eifect of the scanning agent with respect to the thermionic cathode by the received picture signals, the scanning agent of the disclosed embodiment of my invention being the ray it of electrons, the intensity of which is controlled by the received picture signals applied to the control grid 24.

Furthermore, it will be seen that in my improved method of operation for television reception, the respective elemental areas 01' a screen are successively bombarded with electrons such, for example, as the successive bombardment of the respective elemental areas A of the screen I2 with the electrons 30 emanating from the adjacent surface of the thermionic cathode screen l8, and further, that during each picture interval'the intensity of' the electronic bombardment and the duration of such bombardment on each of said elemental areas are varied to produce an image of such bombardment on each of the elemental areas A of the screen 12 to produce thereon. an image, is in accordance with or correspond .to variation in the intensity of the electron ray l5 under control of the picture signals applied to the grid 24-.

Considering my improved method of operation for television reception from another viewpoint, it will be seen that it involves the successive heating to luminescence the respective elemental areas of a screen, such as the elemental areas A of the screen l2, and during each picture interval varying both the temperature to which each of said areas is raised'and the duration of heating such areas to produce an image on this screen. In the disclosed embodiment of my invention, the temperature to which any particular elemental area A of the screen I! is device, the screen raised during each picture interval is proportional to the intensity of the electron ray l6 at the instant it strikes or lbomb'ards the adjacent and. complementary elemental area of the thermionic cathode screen l8, and the duration of heating of the elemental area A is proportional to that part of the picture interval elaps ing before the adjacent and complementary elemental area of the screen 18 cools to the point whereat the electron emission 311 ceases.

. In the construction of my improved scanning I8 can be considered as a source of individual electron rays 30 in number equal to the number of elemental areas of the -image screen I 2 and each serving only one of these areas, the scanning electron ray l6 constituting commutating means for releasing or controlling the effect of the electron rays 30 with respect to the image screen I2.

' In cases where the screen [8 might not have .sufiicient rigidity if it were made entirely of emission begins to take place from the active surface of this screen. This may be done by heating the screen l8 electrically in any well known manner, by bombarding the screen continuously and uniformly with electrons at the required constant intensity for this purpose, or in any other suitable manner. v

It will be understood that the brilliant image produced on the screen l2 may be viewed directly through the transparent end 32 of the tube III, or projected by a suitable .optical system 34 to a remote screen 36 and over an area.

of the latter many times larger than the area of the screen [2.

For the purpose of improving the steepness of the control charactertistic of the scanning device, and speeding up its response to occurring variations in intensity of the cathode ray, a light filter 38 may be placed between the screen l2 and the position from which the image produced on this screen is viewed, or between the screen I 2 and the optical system 34 when the image is projected on a larger screen 36. In explanation of the reasons why such improvement is obtained by use of the filter 38, it should berecognized that, as the temperature of a radiating body isincreased, the wavelength at which the maximum intensity of radiation occurs shifts successively toward a shorter wavelength, and consequently, the amount of radiation in the shorter wavelength portion of the spectrum will be increased. If, therefore, the filter 38 is so chosen that the longer wavelength portions of the visible spectrum are eliminated from the light produced by the incandescent screen l2. the screen will reach a point of apparent extinction more quickly in the presence of the filter 38 because of the fact that it need cool to a lesser extent to reach such a point when only the shorter wavelengths which are radiated from the screen l2 are used. Without the light filter 38, it would take a given period of time for the elemental area of the screen I! to cool from the high temperature for white to the lower temperature. for dark. However, by using the filter 38, which operates to attenuate the visible light adjacent the long-wave threshold of visibility, the temperature to which the elemental area of the screen I! must cool before there is no light of incandescence visible, is substantially higher tially more responsive to variations in intensity of the cathode ray IS in accordance with the received picture signals.

In some cases, it may be desirable to substitute for the incandescent screen l2 a fluorescent screen which may be formed directly on the inside surface of the end wall 32 of the tube, or be in the form of a fine Wire mesh having fluorescent material applied thereto and filling the interstices therein. Such a form of fluorescent screen is disclosed in my pending application Serial Number 4,494, filed February 1, 1935.

It will be understood that various modifications,

within theconception of those skilled in the art, are possible without departing from the spirit of my invention or the scope of the claims.

I claim as my invention:

1. In the art of television reception, the method of operation which comprises developing a ray of electrons, controlling the ray intensity by the received picture signals, selectively heating a thermionic cathode with the controlled ray to cause thermionic emission of electrons from the respective elemental areas of said cathode, and

utilizing the effect of such thermionic emission from said cathode to heat to incandescence corresponding elemental areas of an incandescible screen to produce a visible image on said screen.

2. In the art of television reception, the steps in the method of operation which consist in developing a ray of electrons, controlling the intensity of said ray of electrons in accordance with received picture signals, utilizing said controlled ray of electrons for selectively heating the respective elemental areas of a thermionic cathode to produce a thermal image thereon and to cause thermionic emission of electrons from such areas, and utilizing the effect of such thermionic emission from any particular elemental area of said cathode to heat to luminescence an adjacent and corresponding elemental area of an incandescible I screen to produce on said screen a visible image.

3. A scanning device for television reception comprising a tube provided with an incandescible image screen the respective elemental areas of which become heated to incandescence upon bombardment thereof by electrons, means for developing a ray of electrons, a thermionic cathode having extended area and being disposed between said ray developing means and said image screen and comprising elemental areas complementary respectively to the elemental areas of said image screen and each constituting a source of electrons for bombarding the respective and corresponding elemental area of said image screen, and means for deflecting said ray of electrons to cause the same to scan said thermionic cathode to produce a thermal image on said thermionic cathode.

4. In the art of television reception, the steps in the method of operation which consist in successively heating to incandescence and under control of received picture signals the respective elemental areas of a screen to produce on said visibility by an amount substantially greater than,

the remainder of the visible light is attenuated to produce a modiiled visible image whose total radiation. consists entirely or only a portion of the radiation 01' said incandescent visible image.

5. In the art oi! television reception; the method of operation which consists in developing a ray of electrons. controlling the ray intensity by the received picture signals, scanning a cathode with the controlled ray to cause thermionic emission of electrons from the respective elemental areas of said cathode, utilizing the eflect of such thermionic emission from said cathode to heat to incandescence elemental areas of a screen to produce a visible image on said screen, and at a region between said screen and the position from which the image produced thereon is viewed attenuating the visible light adjacent the long-wave threshold of visibility by an amount substantially greater than the remainder of the visible light is l attenuated.

, 6. In combination, a scanning device for television reception comprising a tube provided with an incandescible image screen the respective elemental areas of which become heated to incandesce'nce upon bombardment thereof by electrons,

and being disposed between said ray developing means and said image screen and comprising-elemental areas complementary respectively to the elemental areas or said image screen and each constituting a source-or thermionic electrons for bombarding the respective and corresponding elemental area oif said image screen, means for defleeting said controlled ray of electrons to cause the same to scan said thermionic cathode to produce a thermal image on said-thermionic cathode, whereby electrons are eniitted for bombarding said image screen; and a light 'fllter disposed at a region between said incandescible image screen and the position from which the image produced v thereon is viewed and operating to attenuate the sion occurs, and an incandescible image screen adapted to be bombarded by thermionic electrons emitted from said cathode at points substantially corresponding to the points from which sald ther mionic electrons emerged from said cathode to produce an incandescent image on said image screen. I

JOHN C. BATCHELOR. 

